1. Field of the Invention
The present invention relates to monitoring systems for vehicle air brake systems for both parking brakes and foot brakes.
2. Prior Art
There are a wide variety of monitoring systems for air brakes and associated actuator assemblies with particular attention being directed to brake adjustment.
Virtually all braking systems experience wear during use, with that wear in turn causing a certain amount of free play in the brake mechanism which reduces stopping ability of the vehicle. Such free play requires some form of periodic manual or automatic adjustment of the brake mechanism in order to have the brakes operating at or near peak efficiency. Conventional passenger cars have hydraulic systems that are monitored and adjusted by automatic systems. Hydraulic brake systems which lack such adjustment features still provide the driver with a fairly good indication that brake adjustment is required in the form of excessive brake pedal travel.
Hydraulic braking systems, even of the power assist variety, are not adequate on larger vehicles such as buses, large trucks and tractor trailers. Such larger vehicles commonly employ air brakes where brake pedal activation controls a valve that releases compressed air from a storage tank. With such air brake systems, pedal travel is no longer reliable for determining the need for brake adjustment, as the air is compressable. Automatic brake adjusting schemes are available for larger vehicle air brake systems, but failure of these mechanisms can occur without the operator knowing of such failure until an accident occurs. Such a failure problem is compounded by relying entirely on the automatic adjusting devices by the operator. Further insight into the nature and severity of this problem may be found in the article entitled "The Importance of Maintaining Air Brake Adjustment" authored by Radlinski, Williams, and Machey, published as a Society of Automotive Engineers Technical Paper Series in 1982. Briefly this paper points out that something on the order of fifteen percent (15%) of the air braked vehicles on the road are in an unsafe condition due to brake misadjustment. This article concludes with a number of suggestions to improve the brake adjustment situation.
In addition to brake adjustment issues there are also important concerns regarding component overtravel and/or failure in a manner that will prevent proper brake operation. Merely knowing the brakes are out of adjustment does not indicate other possible problems with the brakes. The prior art brake adjustment indicating devices do not indicate other problems that may be associated with the brakes and Actuator Assemblies. See for example U.S. Pat. Nos. 5,226,509; 5,207,299; 5,206,625; 4,800,991; 4,757,300; 4,583,071; 4,279,214; 3,997,887; 3,339,676; and 3,298,466.